AC over DC 7

what do you mean by "more powerful"?

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(2B)+(2B)' ?

and is this specific to motors? if not I suggest another forum

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(2B)+(2B)' ?

Sorry for being vague. I was watching the "War of currents" yesterday, and they were talking about How D.C needed stations every 2 mile how AC could be transmitted over 100 or miles ( Step Up Step Down) etc etc. I wanted to know the science behind the AC signal. I was always fascinated but failed to understand the electrical properties. I just want to know, the mathematics behind why DC, is inferior for power distribution than AC.

If DC is inferior for power distribution, then why are the highest capacity bulk transmission lines DC?

It all has to do with the cost of changing voltages. Easy with AC, difficult with DC.

That is closer to religion than scientific opinion. In fact, LONG distance power transmission lines are actually DC in many cases. The truth is, both have their place in the world, each with advantages and disdvatages.

The reality is, the "war" between Tesla / Westinghouse and Edison was more about a battle of personalities than about specific technologies. Edison proved the value of having electricity as a simple and readily available energy source for common households, but thought that it was his alone to control and distribute at his will and profit. When Tesla and Westinghouse came up with a simpler way to distribute it more widely and NOT use the infrastructure plans that Edison had already been contemplating, he appears to have become bitter and vindictive rather than embrace it as am improvement, which he (or rather his legacy company GE) ultimately did. DC is still superior in some aspects and applications to AC, and vice versa. It's just not black and white, but "shades of grey" makes for dull reading and boring documentaries.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

Edison vs Tesla (Westinghouse). Start reading.

Thank you for the good schooling you all.

So i never understood electricity or the whole science. Now could you tell me how i can understand any books that will help me. Where do you people suggest i start. I am taking baby steps again.I want to learn.

Thanks
Bharat Chandra Penumutchu

This forum is really for practicing Electrical Engineers, so don't be surprised if you get bumped off by the admins. But before that happens, hopefully you will see this. It's a link to a set of free on-line courses offered by Siemens. Start at the very beginning, the one that says "Basic Electricity", because that one starts with DC (simpler to understand) and works you up to AC, and explains why. After that you can choose to go further if you want to, but to be honest it starts to get fairly industrially oriented after that. Still, I have not found anything better for free.


Good luck.

By the way if you really are a "Computer" guy as you seem to have registered as, there is a companion forum to this one called Tek-Tips.com that you might find interesting.


"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

The history of electrical systems is quite interesting. Many are surprised to find the tiny towns in the middle of nowhere had electricity before larg cities. Mining operations were the early aaptors of this technology. The first high tension line was in Teluride CO. If it didn't work they figured they could turn it into a ski lift!

I am sure, i know it is annoying for asking generic questions. Actually. I will be very careful in what i post, see that Siemens website what what i was talking about. Actually i am into WiMAX and Networking . But along the way i also want to understand nature. Because Electrical Engineering is like simply playing with Nature, so i do want just want to know,that they are simply using OFDMA for WiMAX,i want to understand in depth why and how they use it. I want to understand in depth.

Pick up a basic electrical book - something Electricity for Dummies and go from there. (Not really sure that book exists - but you get my drift)

Any/all types of electricity I find quite fascinating - from static to lighting to AC/DC.

By the way I think most electric chairs are DC. For a given voltage - it will kill you much faster...

There are some basic facts relative to the argument of AC versus DC that need to be recalled.

When Edison built the Pearl Street station, the main load was street lights. DC generators delivered 110 V. At some point, you had to add another generator (dynamo), but you still couldn't deliver 110 V much beyond a clustered area.

Westinghouse followed in a different part of New York City with his AC system. Whether the voltage was 110 V AC or DC wasn't the issue. As with Edison's system, you couldn't go very far with low voltage delivery - whether it be AC or DC. Tesla's development of the transformer enabled the AC system to have an unfair advantage at that time because you could step up a delivery voltage and be able to transport the power much greater distances. The DC system didn't have any means of doing this.

I won't get into the high voltage transmission area except to note that the argument basically compares the costs of the lines and terminal equipment to see what distance does the DC system become justifiable over long distance AC. In the past, it had been in the neighborhood of 300 miles or so, that is, above 300 miles, the DC system will be the lower cost. Today, I'm sure the breakeven distance has come down.

To say that one is more powerful than the other is a naive argument since both long distance HVAC and HVDC rely on an AC transformer.

Maybe these fundamental points with help clarify things for BharatNT2IE.

A lot of engineering is about doing more with less. Wire is expensive. With bigger wire you have less loss. Power is volts times amps. If you transmit electricity at higher voltage the current is lower for the same amount of power. AC transformers easily change voltage to a higher value. This made sending power long distances cheaper. Early on there was no way to do this cheaply with DC. As demands on the grid have increased they have raised the voltage on transmission lines. This has now reached the practical limit. With the first transmission line in Teluride CO they learned something interesting. The wire was so small in diameter that the wire glowed at night. They had to increase the wire diameter to stop it from glowing. The actual peak voltage of AC is much higher than the stated RMS value. Transmitting DC at the equivelent Peak AC voltage allows more power to be sent on existing lines. It is now becoming practical to have DC to AC converters on transmission lines. That show may have implied that AC was the end all answer. That is not true. Which is used is based on practical considerations.

Thank you very very much.

I think it's important to point out to the OP that AC power transmission at High Voltage [using transformers] made generating electricity at Niagra Falls ["Free Hydro-Power"]and transmitting the power to New York City practical [reasonable power losses].

It's also important to stress that three phase power and the induction motor really cannot be separated from AC Power. All invented by Tesla.

magoo2:

Edisons first station at Pearl St. used the 3-wire system (his invention) that is 110V+, neutral, 110V-, giving 220V across the outer conductors. Still in use today as AC: 120-0-120V giving 240VAC.

To get the 220VDC, two dynamos were connected in series, with the center point grounded. There was also a 5-wire system +250, +125. neutral, -125, -250, last used in San Francisco, CA, Who invented this is unknown. No longer exists.

BTW: before Edison invented his famous bulb, there were already arc-lighting systems in wide use, The arc lights were on a series DC circuit, running at constant current and variable voltage, which could go up to well over 500 V.
Not a thing for the bedroom or indoor use, only outdoor.

rasevskii

I maintained series incandescent street lamps in the late sixties. Some circuits could hit about 8000 Volts if they went open circuit.

Bill
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"Why not the best?"
Jimmy Carter

OperaHouse:

I don't believe you are correct as to why high-voltage DC transmission is sometimes used. The energy dissipated in a conductor over a cycle of AC is the same as the energy dissipated in DC over the same time period for the same power transmitted. With AC, the power dissipation is sometimes higher, sometimes lower, over the cycle, but it averages the saem, and the thermal time constant of the conductor is far greater than an electrical cycle, so there is no effective difference.

Rather, the problem with long-distance, high-voltage AC transmission is due to AC's greatest strength: the ease of inductive coupling. AC transmission lines couple inductively to the ground, transferring energy into the ground, producing parasitic losses. The amount of these losses is very low over short distances provided proper precautions are taken -- sufficient height off the ground given the voltage, etc. But over very long distances -- hundreds of kilometers -- they can add up to be come very significant. The problem with underwater cables is much worse.

In these cases, it can make sense to shift to DC transmission, balancing the increased losses due to the conversion from AC to DC, then DC to AC, against the reduced losses along the way.

Perhaps my point wasn't clear. Say the line has 1 Meg V AC at 50A. That 50A line loss is the same for DC. However at 1.4 Meg V DC you have sent a lot more power down the line using same equipment.